In DE-OS No. 23 29 022 a variable control mechanism for the guide blades of a gas turbine is described, the guide blades of which are pivotable around pivot axles. To pivot the guide blades, they are provided in the area of their discharge edges with lateral pins which engage axial guide grooves in an adjusting ring. The guide blades may be pivoted between end limit stops by means of the adjusting ring, but the guide blades are not freely pivoting. The guide blades are forcibly guided in each operating range of the gas turbine according to the setting of the adjusting ring.
In DE-OS No. 24 55 361 an adjustable control mechanism of a turbine or compressor is described, wherein the blades are guided on the one hand in a housing and on the other hand in an adjusting ring. The adjusting ring is variable between two stationary stops. The guide blades are thus forcibly guided by mechanical means, which requires a relatively large mechanical effort to mount each guide blade around two pivot axes and to provide an eccentric member, an elongated hole, or the like. Further, external adjusting forces must be applied in two directions to adjust the guide blades.
A turbocharger with a variable control mechanism is described in U.S. Pat. Nos. 4,179,247, wherein the pivot axles of each guide blade are fixedly connected to a lever so that they rotate together. These levers are operatively connected with an adjusting ring provided with an elongated hole or the like, so that as the adjusting ring is rotated, the lever and thus the associated guide blades also rotate accordingly. Thus, in this device forced guidance is again employed, so that adjusting force must be applied in both adjustment directions. The direction of flow of the flow medium is determined by the control mechanism by means of the forced guidance. It has been found that, particularly in the partially loaded state or partial load range of the engine charged by the turbocharger, power consumption is adversely affected by clearance and impact losses.